In electronic systems, individual circuit components are typically protected from short-circuiting and excessive currents by a fuse or a circuit breaker interposed between the component and a power supply. Large numbers of such protection devices may be found within any given system, depending upon the number of individual components contained therein. This has given rise to the need for fuse and circuit breaker status indicators which allow for the easy and rapid location of a tripped, failed or "blown" protection device within an electronic system. Typically, these indicators are incorporated into a fuse holder or circuit breaker housing, and trigger an alarm which serves to alert service personnel that a particular protection device has blown or tripped; the alarm can be an electromechanical flag, a light emitting diode ("LED"), a lamp, or an audible signal.
Such fuse and/or circuit breaker status indicators must remain electrically isolated from the circuits being protected to ensure they do not affect the performance of the protected circuits. In addition, the indicators must not significantly compromise the isolation between the protected circuitry and the power source after a fuse has blown or a circuit breaker tripped. Furthermore, the indicators should be capable of being easily tested, while on-line, to determine if the particular alarm (i.e. a flag, LED, lamp, or audible signal) is operational. In electronic systems employing large numbers of such status indicators, it is often preferable to test all the indicators at once.
Present circuit protection device status indicators fail to provide the desired degree of isolation from the protected circuity, maintain the isolation between the protected circuit and the power supply, and allow for the easy, simultaneous on- line testing of large numbers of indicators.